Chapter 22 Flashcards
Quality Assurance
is the routine, periodic evaluation of a system to guarantee optimal image quality
It is a medical and legal necessity
Quality Assurance Requirements
Assessment of system components
Repairs
Preventative maintenance
Record keeping
QA Goals
Proper operation of equipment
Detect gradual changes in performance
Minimize downtime
Reduce the # of non-diagnostic exams
Reduce the # of repeat exams
QA Devices
Tissue equivalent phantom
Doppler phantom
Beam profile/slice thickness phantom
QA is based on Objective Standards
Unbiased
Factual
Repeatable results; regardless of the tester
Tissue Equivalent Phantom
Box filled with medium that has the same PS and attenuates, scatters, and presents echogenicities similar to soft tissue
-Embedded in the medium are strategically located pins (strings, rods), mock cysts and masses
Doppler or Flow Phantoms
Used to evaluate Doppler systems
Modern include circulation pump which propels fluid through vessels embedded in a tissue equivalent phantom
-assess characteristics of all Doppler modalities including PW, CW, color, and power mode
Slice Thickness Phantom
Used specifically to evaluate slice thickness which determines elevational resolution
-the display demonstrates the beam geometry or thickness
Sensitivity
the ability of the system to register low level echoes
Normal sensitivity
is the gain, TGC, and power setting where all pins, cysts and masses are accurately displayed
It is recorded and should not change from test to test
Maximum Sensitivity
is evaluated by setting the power and amplification to maximum and determining the maximum depth of tissue like texture
This depth should not differ from one routine evaluation to the next
Dead Zone
is the region close to the probe where images are absent due to the time it takes to switch from transmit to receive
Registration Accuracy
is the ability of the system to place reflections in the proper positions
Range or vertical depth calibration
describes the systems accuracy in placing reflectors at correct depths
-An error could indicate system malfunction or the PS in phantom fell off 1,540 m/s
Horizontal calibration or registration accuracy
is the ability to place echoes in their correct position horizontally across the display (perpendicular to the sound beam)
Distance Measurement Accuracy
The distance between two vertical and horizontal pins should be measured to check the digital calipers
Focal Zone
The focus is adjusted (depth, #) and the lateral resolution assessed in the region effected
Axial Resolution
is evaluated by scanning a set of closely spaced pins positioned front to back in the beam
Lateral Resolution
is evaluated by scanning a set of closely spaced pins positioned side by side in the beam
Compensation Operation or Uniformity:
Two same reflectors in phantom are located at different depths. TGCs are applied to ensure equal echodensities can be displayed
Mock cysts and solid masses:
the tissue equivalent phantom is used to evaluate the dimension, texture, and fill-in of cysts
Display, Hardcopy Output, and Grayscale dynamic range
Power, gain, compress are adjusted and grayscale change evaluated
Adjusting contrast and brightness only effects that monitor not stored or archived images
Comparison Test
is the test you want to look at
Sensitivity
the ability of the comparison test to detect disease
TP/ (TP + FN)
Specificity
The ability of the comparison test to detect the absence of disease
TN/(TN + FP)
Accuracy
the percentage of times the comparison test is right
(TP+TN) / (TP + FP + TN + FN)
Positive Predictive Value
the % of time the test correctly predicted the presence of disease relative to the total number of time the test predicted disease
TP/(TP + FP)
Negative Predictive Value
the % of time the test correctly predicted the absence of disease relative to the total number of times the test predicted no disease
TN/(TN + FN)
